Have never experienced this but a friend of mine who had alopecia (not from dreads she was just born with it) used a cream on her bald spots and it solved the problem, you could ask your doctor about any creams you can use? Good luck

update: so I have brushed out dreads and made new skinny ones. I have around 40 something now. There's just this one dread (the first one I made, significantly older than the rest) that's way too fat but its super tight and no matter how much I try to comb it it won't come out. However on the root there is a very obvious partition as if it were two separate dreads forced into one my question is will it naturally separate into two smaller dreads over time or will the two separated sections just continue to grow together forever or until I use whatever last resort it takes to comb it out?